The goal of Boxworld is to complete all 100 levels by pushing all of the boxes on each level onto the circles. It's single player, so just click Download to play.
The idea for this game isn't mine; I just remade an old game with the same name.
Controls:
Arrow keys - Move your character
Escape - Exit the game
W - Retry your current level
E - Go to a different level
R - Undo your last move